With peace throughout Ninjago, Kai and the other Ninja fell out of training and instead spent their time playing video games. After a three hour marathon, they are interrupted by Wu who unplugs the TV. He encourages them not to put off tomorrow what could be done today, and to start training again to
prepare for his brother's return to Ninjago. Kai reminds his Master that if Garmadon is to show up, they have the Tornado of Creation. Wu sighs and tells him and the others that they have barely scratched the surface of unlocking their True Potentials. Cole turns the tv back on, and the Ninja continue playing.
At that moment, Nya rushes in, bringing word that Garmadon was spotted in Jamanakai Village. The out-of-shape Ninja rush out the door and down to the dragon pen where Kai mounted the Fire Dragon with the Nya's help.
Eager to get back into the fight, the Ninja race each other to Jamanakai Village. Upon arrival, Kai argues with Jay about who had arrived first. They were interrupted by the sound of evil laughter from the village, and they draw their weapons. They approach the village but are surprised to find that it was, in fact, Lloyd Garmadon, the dark lord's son, who was causing trouble. Lloyd threatens to release the serpentine, an ancient race of snakes that once ruled Ninjago unless they give him candy. The Ninja tie him to the top of a sign and embarrass him in front of the villagers as they mock him by eating candy.
As they prepared to return to the monastery, Kai discovered a scroll in Wu's bag which he had taken by mistake. They read it and learn of the Prophecy of the Green Ninja. It is said that one Ninja will rise above the others and become the Green Ninja. The scroll is also inscribed with drawings that are identical to the four Ninja, with a fifth Ninja in the middle. Kai believed himself to be the Green Ninja, as did the others, so when they returned to the monastery, the four Spinjitzu masters challenged themselves to a tournament for the title. Kai faced off against Jay in the first round and won, thus moving on to the final round against Cole. However, the tournament ended when Kai lost control of the Sword of Fire and the Ninja were scolded by Master Wu.
Determined to be the Green Ninja, Kai and the others devoted themselves to training. They were soon ordered back to Jamanakai Village and find that Lloyd had unleashed the Hypnobrai tribe of Serpentine. Kai once again mounted the Fire Dragon and upon arriving at the village, met up with Nya. The Ninja find that the Hyprobrai have the ability to hypnotize their victims into doing their bidding, and were doing so to the villagers. After discovering they would need the anti-venom from the Snake General's staff to save the village, the Ninja split up and after a fight with the snakes, sent them retreating. After the villagers had been cured of their hypnotism, Kai presented Wu with the staff and apologized for their lazy behavior earlier. With a new threat now upon them, Kai and the others returned to the monastery determined to unlock the secrets of their Golden Weapons and to reach their True Potential.
In the days that followed, Kai devotes himself to training at the monastery. While he was practicing Spinjitzu, Zane iced the course over, causing Kai to slip. He complained about Zane's strange behavior to Jay and Cole, only to be approached by Master Wu who noted that brothers are often different. Kai remembers one night when he went into the kitchen for a midnight snack, only to find that Zane had consumed everything but the cheese. The Ninjas' conversation was interrupted by the arrival of the Mailman who had a fan letter for Kai, and other mail for Cole and Jay. They make note that nothing has come for Zane, and Zane reveals that he has been an orphan all his life.
That night, Kai and the others gathered in the dining room and were surprised to see Zane emerge from the kitchen wearing a pink apron. The Ninja laughed, and Zane failed to find it amusing. Cole dumps a plate of food on Kai's head and shortly after a food fight breaks out.
The next day, Zane tells the others that last night he followed a mysterious bird to Lloyd's Treehouse Fortress. Together, they head into the Forest of Tranquility and find it exactly where Zane said it would be.
Determined to destroy it before it becomes operational, Kai and the other Ninja snuck into it and destroyed its supports. They reached the last support, but Cole, who was hypnotized by a serpentine earlier, turns on them. Before long, Master Wu came riding in on Flame playing an ancient flute, which canceled the Serpentine's powers. The group returned to the Monastery on Flame and discovered the Serpentine had set fire to it in order to steal back their staff.
Zane asked Shard to put the fire out but, the Monastery was beyond repair. Kai and the others verbally attacked Zane but Master Wu caught them reminding them that Zane was their teammate and had them apologize. Before they could, Zane flew off on Shard. Kai and the others assume that he was so hurt by their words that he ran away. Later on, the Ninja eat around a fire on a cliff, homeless, until Nya noticed Zane entering the camp. He reveals to them that he was not hurt by their words, but saw the falcon again, and followed it to an abandoned ship. He told them that was their new home, and he made them dinner.
Kai and the others joyfully run towards their new home, ready to eat Zane's home-cooked food.
After arriving on Destiny's Bounty they find that it is in disrepair. Master Wu makes the Ninja clean up their new home while he runs an errand with Nya, which they are reluctant to do.
They proceed in cleaning it up, dusting the sail, cleaning the cabins, and reworking the electronics. When finished, they put all the trash and junk in the bin outside.
Later on, while the Ninja are relaxing, Jay's parents, Ed and Edna, arrive. They are given the tour of the Bounty by Jay, but he insists that they leave due to the threat of the Serpentine. While there, they reveal that Jay was born in a junkyard, a fact which Jay is embarrassed about. Eventually, his parents are reluctant to go but leave before dark. Before going they implore that Jay visits them sometime soon. Jay agrees, and they head out.
The next day as they are doing work on the brig, the other Ninja try to convince Jay to visit his parents. Although he is reluctant at first, he agrees to go. He goes to mount Wisp but finds that he has no interest in going anywhere. Master Wu tells the Ninja that their dragons are molting, and are to return to the Spirit Coves in order to reach maturity. The Ninja are disheartened, and Jay asks Nya to accompany him on the long walk. Kai and the others think he wants them all to go, and so the whole team accompanies him.
When the Ninja arrive, they find Jay's parents nowhere to be found, until they find them locked in an old refrigerator. They learn that another tribe of serpentine, the Fangpyre, had bitten Jay's parents and infected them with venom, slowly turning them into serpentine.
Kai and the other Ninja are ambushed by the Fangpyre, who, lead by Lloyd, have turned the whole junkyard into a snake infected area. Kai and the others defeat the snakes and attempt to escape. Master Wu tells them that they can get out of there faster by turning their Golden Weapons into vehicles. Kai turns his sword into a bike and drives away as the others do the same. They escape with Jay's parents after stealing the Snake General's staff, and return to the Bounty, and cure Ed and Edna with the anti-venom. The Bounty is rocked to the side by one of the Fangpyre helicopters, and they drop the staff, returning it to the serpentine and Lloyd.
Zane is woken up with a start one morning and recalls that he had a dream. Kai and the others ask him what it was about, and he tells them that he saw the Green Ninja. The Ninja implore him to elaborate, but Master Wu interrupts and reminds them that it is time for training.
On the deck, Wu teaches them different poses, all the while they are ignoring him to learn more about the dream. Wu catches them slacking off, and tells them that as punishment they must train all day and come up with the answer to a riddle, "What is the best way to defeat an enemy?" Kai fails to interpret the riddle along with the other Ninja, so Master Wu leaves them to train.
Zane finishes telling them about the dream, and Kai assumes himself to be the Green Ninja, due to his fists being aflame. The Ninja argue over who is the real green ninja and get back to training.
The Destiny's Bounty takes them there, where they drop through the roof of the building on an anchor. Kai and the others chase the panicking Lloyd through the building until they reach the roof. There, Pythor steals Lloyd's map of the Serpentine Tombs and disappears. The Ninja take Lloyd back to the Bounty and find that Master Wu is reading him a bedtime story.
They are confused as to why he is read a bedtime story after causing so much trouble, and Master Wu reveals the answer to the riddle- the best way to defeat your enemy, is to make him your friend.
Kai discovers one day that all of his high scores have been replaced by Lloyd who at the time blamed it on Cole.
Lloyd screws with the other Ninjas' hobbies as well, ruining Jay's robot, Cole's chili, and turning Zane's gi pink, but he is eventually caught, and reprimanded by the Ninja. They try to snitch on him to Wu, but he reveals that he put Lloyd up to it to teach the Ninja "the destructive power of rumors."
They arrive in the Toxic Bogs and find that the tomb has already been opened. They soon find that they are being ambushed. Kai is intoxicated with Venomari venom and begins to see elves and gingerbread men attacking him. Jay attempts to protect him while Kai is trembling from the visions. Cole and Zane arrive but are followed by Pythor and the Constrictai. As the two tribes surround them, the Ninja believe they will not survive the next attack.
Kai hallucinates that a rope is in front of him, only for an actual rope to appear moments later. Suddenly, a mysterious Samurai in a massive robotic mech appears and scares away the Serpentine. The Samurai saves the Ninja but knocks them unconscious. They are soon saved by Wu in the Bounty.
Back on the ship, the Ninja are eating dinner (while Kai is still intoxicated,) while telling Lloyd and the others about the mysterious samurai. Kai insists that he had weapons coming out from every part of him, but the Ninja remind the others that he was sprayed with the Venomari venom.
They get an alert later on that the Serpentine have been spotted in Ninjago City, and the Ninja quickly ascend there, expecting to find a massive serpentine gathering in the streets (at this point Kai's intoxication wears off.) They find that the Serpentine have gathered underneath the city, and venture below.
They find Pythor giving a speech to the serpentine tribes, attempting to unite them. The Ninja know this is a bad sign, so they use the destructive power of rumors to try and ruin his assembly. They are eventually caught and are chased throughout the sewers. Kai, Cole, and Jay are quickly captured, and Zane is left trying to escape from them.
After using his pink gi to distract the snakes, he breaks out Kai and the others and they escape, having ruined Pythor's plans.
Later on, back on the Bounty, Lloyd apologizes for messing with the Ninja's things and reveals that he has cleaned Zane's gi.
The Ninja are eating breakfast talking about the Samurai when Kai offers the other Ninja a bet: whoever finds the identity of Samurai X, they are the best and the Green Ninja.
The Ninja agree to the terms and are interrupted by the arrival of the mailman, who has brought them their new Ninja suits. As they are checking the new merchandise, they get an alert that some snakes were spotted at Mega Monster Amusement Park. They put on their new suits, and arrive at the park to find that the serpentine have already been apprehended by the Samurai.
The Ninja make it their mission to catch this samurai, and they split up separately to do so. Kai attempts to capture him when he finds him in the Forest of Tranquility but the he quickly captures Kai in a net.
Later, when it's his turn to look after Lloyd, he drops him off at an arcade, then leaves, hoping to find the Samurai. After finding Lloyd missing, the Ninja go looking for him at The Lost City of Ouroboros.
The Ninja get trapped in a cage that Pythor set up knowing they would come, and steals their golden weapons. He forces them to battle the Samurai X to entertain the other Serpentine, and they find out that they are no match for him.
In a strange turn of events, the Samurai helps them escape whilst stealing back their Golden Weapons.
The Ninja and Samurai X crash land somewhere nearby, and are left scattered. Kai regroups himself and finds that he landed near the Samurai. He walks up to him and finds that their secret identity was none other than his sister the whole time! Nya implores him that he doesn't tell the others her secret, to which he tells her about the bet he made with them.
He sees what this means to her, and agrees to keep quiet. Nya gives him back the Golden Weapons, and he and the Ninja return home separately than Nya.
Back at the Bounty, the others interrogate Kai about the encounter he had with the Samurai. Stumbling over her pronouns, he tells them that she- he, just handed him the Golden Weapons and left, which was a lie. The Ninja have a hard time believing this, but carry on their meal.
As the Ninja continued to train, they became capable of impressive feats; Kai was able to run across a long path of red-hot coals with no ill effects. Later, he timed Zane as he sat underwater, expressing bewilderment as his white-clad ally remained beneath the waves for over ten minutes. After Zane finally returned to the ship, Kai and the others began speculating whether they had reached their full potential, and decided to ask Master Wu before they jumped to conclusions.
When Kai and the others found Master Wu, he was packing his things, seemingly in preparation for a journey. Kai presented the Ninjas' question, but Wu quickly shut down the notion. He tells them that when they find the key, they will know.
They change the topic, and ask their Master about the katana he is holding, and he tells them the story.
When Wu and Garmadon were young they were the best of friends. One day while they were playing sword fighting in the monastery, Wu's blade was knocked over the fence. Fearing that their father would be mad, Wu refused to go and retrieve it. His brother reminds him not to put off until tomorrow what can be done today, and goes after it himself.
Garmadon hops the wall, and reaches for the blade, only to be bitten by a snake. He falls ill, and Wu reminds the others that that snake was the Great Devourer, the same snake that Pythor wants to resurrect. . . Its venom turned his brother into the Dark Lord.
After his story, he says that he is leaving to find someone who can be of aid in finding Lloyd.
Later, Kai and the others put posters up to find the Four Silver Fanglades, which Pythor needs to resurrect the Devourer. Zane stops putting up the flyers, and notices the Falcon. The others remark that whenever they follow it, it brings them good fortune, so they chase after it. They follow it through Ninjago, hoping it will lead them to a Fangblade.
After chasing it for miles, Kai and the others begin succumbing to exhaustion, telling Zane to continue following the Falcon into a snowy woodland.
The Ninja eventually pick themselves up and find Zane to be horrified by something he's uncovered in an old workshop; Zane is an android. Kai and the others still accept him and don't seem bothered by the revelation, they even think it's pretty cool (with Jay referring to Zane as a "Nindroid.")
The other Ninja leave Zane to think and immerge back outside. Creatures referred to as Treehorns attack them, and they are quickly defeated by them. Zane returns and finds his friends in trouble, and helps fight back.
The queen treehorn emerges, but using his newfound powers, Zane freezes the Queen as the other Treehorns retreat. While the other Ninja are happy for Zane for being the first to unlock his True Potential, Zane proclaims with confidence that they are going to find Pythor.
While watching Nya explain the venom process of a Fangpyre, Jay tries to impress her with men's cologne but finds out that Kai and the others pranked him by giving Jay perfume, which Nya is allergic to.
Later on, the Ninja find that a Fangblade is at Mega Monster Amusement Park, and prepare to go there to acquire it. Jay attempts to go on a date with Nya at the park but Kai warns him not to, telling him "to get his priorities straight."
The Ninja discover a ride that has Serpentine activity near it. The Ninja discover the Serpentine excavating the Fangblade and Kai declares a fight. Kai gains the upper hand in the fight along with the others but a mistake on Zane's part causes them to get frozen from one of his attacks. Kai and the others escape their confinement and Jay is revealed to have gained his True Potential while Nya is discovered by all the other Ninja to be Samurai X.
Kai brags that he is the first to have found out and therefore should be the Green Ninja, but the other Ninja claim to not remember ever discussing that.
The Ninja, upset at losing the Fangblade, brainstorm for where the next Fangblade would be. Cole brings up that he knew about a trophy called the Blade Cup that seemed to be a Fangblade that his father once won at a talent show.
The Ninja go to Cole's father and disguise themselves as dancers as to not cause suspicion around Cole's dad, who is unaware of Cole being a Ninja.
They discover the Blade Cup is located at a talent show and enter it as a cover to steal it. Lou trains Kai and the others to dance,however, the Serpentine have also discovered the Fangblade's location and disguise themselves as people in the audience, judges, and performers.
The Ninja are preparing inside the backstage of Concert Hall. However, Jay and Kai begin arguing when they continuously mess up the routine. Cole interrupts by saying that they will be leaving soon after their theft, Jay replying that they should try to win it. Having overheard the conversation, Lou confronts them about it. Cole takes the opportunity to explain to him the situation of having lied to his father for many years, revealing that he is a Ninja. He informs Lou that if they do not steal it themselves, the Serpentine will instead. Regardless, Lou is unaccepting of his son for wanting to steal the prize, storming out of the room. While the Ninja comfort Cole, a group of disguised Serpentine called the Treble Makers appear backstage. Kai hears Pythor's voice from the crowd, peering out from behind the curtains to see the General among the judges.
The other judges say that Pythor looks nothing like how he did in the photo, Pythor coming up with an excuse before the voice of the former judge alerts the others of his situation from Pythor's stomach. The other judges gaze in disbelief, Pythor quickly persuading the noisy judge to quiet down.
Kai tells the Ninja of the Serpentine, and when Jay finally agrees to stealing the Blade Cup, Cole instead decides that they will win it.
The Treble Makers sing on stage, the crowd booing as Pythor gives the performance a perfect ten. The other judges each give it a six, but Pythor intimidates them into flipping their scorecards.
The Ninja are called up on stage, though as they linger backstage, Zane confesses to having butterflies in his stomach. They then share a few encouraging words among themselves, going on stage by the name of Spin Harmony. As they dance in perfect sync, Skales orders the Hypnobrai to attack. However, the attack only intensifies their performance, the Ninja incorporating defending themselves in their routine. When the Fangpyre join the ambush, Cole then uses the opportunity to perform the Triple Tiger Sashay with success.
The Ninja win the talent show and Cole's father is proud that they won the trophy without cheating as the Serpentine tried to do. Pythor then attacks and nearly kills Cole's father, but Cole protects him and gains his True Potential while the Serpentine manage to steal the Fangblade, making Kai the only Ninja left to find his True Potential.
Master Wu finally returns and surprises them by bringing Lord Garmadon, who has now grown four arms.
Kai attacks Garmadon, assuming the worst, but Master Wu reveals that he is helping them search for Lloyd and orders the Ninja to respect him during their temporary alliance.
Kai gets more skeptical about Lord Garmadon and at one point overhears a conversation about the Green Ninja between Nya and Master Wu. Lord Garmadon discovers Kai eavesdropping and the two fight, only to be broken up by Nya and Master Wu.
Later on, Kai searches for the Golden Weapons and discovers Garmadon is holding them. Thinking he is stealing them, Kai battles Garmadon and "wins." He expects to have unlocked his true potential, however, Garmadon reveals that he allowed himself to be defeated, as he was only fetching the weapons for the Ninja since they were heading over to their destination; this was confirmed when Master Wu told Kai that he was the one who told Garmadon to fetch them. Realizing this, the other Ninja scold Kai for his foolishness, leaving him humiliated. Despite the situation taken care of, Kai still retains his suspicion towards Garmadon.
After discovering the next Fangblade is located at the Fire Temple, the Destiny's Bounty arrives there and the group travels inside. They watch as the Serpentine dig for the Fangblade, Jay quickly pointing out Lloyd's location in a cage. Rattla uncovers the Fangpyre Fangblade, much to Pythor's pleasure. While Pythor gleefully gazes at the Fangblade, he notices the Ninja in the reflection and orders the tribes to attack.
The Ninja quickly fend them off, though as Pythor leaves the Temple, he commands Bytar and Chokun to drill holes in the walls to allow the rising lava to quicken. Jay announces that they must leave as the Temple is becoming unstable, but Lord Garmadon runs after the Serpentine in an attempt to retrieve his son. Seeing that Lloyd is causing the trouble, Pythor orders the Serpentine to get rid of the caged boy by dropping him to the landing below. Lord Garmadon continues to fight the Serpentine to get the cage, finally reaching it and pulling up his son before his cage could fully melt in the lava.
Kai then rushes up the steps in order to obtain the Fangblade, flinging the Sword of Fire at the Fangblade to impales it in the wall. A furious Pythor attempts to pull it out, but Skales alerts him that they must leave at once, Pythor complying as lava shoots up at them. Everyone except for Kai meets up at the exit and Lloyd calls out to his missing teammate as Kai makes his way to the Fangblade. However, the ground beneath Lloyd breaks loose, causing him to fall down to the lava below. The group watches in horror as Lloyd stands on the sinking piece of land.
Meanwhile, Kai finally pulls his sword out of the wall, but the Fangblade falls down below, landing just above the lava. Kai tries to grab it but chooses to save Lloyd instead when the latter cries out for help. He grabs Lloyd and tries to escape, but they become surrounded by lava spewing into the air.
Everyone else reaches the Destiny's Bounty, the entire team distressed as they see lava exploding out of the volcano. In the middle of their remorse, they suddenly see a fireball appear from the volcano, which floats toward the Destiny's Bounty to reveal Kai and Lloyd inside. Having unlocked his True Potential, Kai stands proudly, only to fall to the ground in exhaustion.
Kai gains his True Potential and realizes that he wasn't meant to become the Green Ninja, but to protect him. After reuniting with Lloyd, Garmadon genuinely thanks Kai for saving Lloyd, who is then revealed as the Green Ninja. Upon realizing this, Kai expresses an empathetic face, seeing how complicated it would be for Lord Garmadon and his son to be fighting each other in the future for the sake of Ninjago. He now realizes that he and his fellow Ninja were never meant to become the green Ninja, but to protect him.
The episode begins with the Ninja cornering Spitta and forcing him to give them information on Pythor's whereabouts. Spitta tells them that they are days behind him, as he is already on the way to the next fangblade.
Back aboard Bounty, Lloyd suggests that while Pythor is away, they should go to the Serpentine's inner sanctum to retrieve the other three Fangblades. The Ninja quickly find the snakes inner sanctum hidden inside the Constrictai Tomb, and Lloyd and Lord Garmadon stay behind.
Inside the tomb, the Ninja attempt to defeat the snakes, but to no avail. The Ninja are quickly captured and are forced to contact Lloyd for help.
Lloyd and Garmadon get into an argument, resulting in Garmadon leaving without telling where he is going. Lloyd then gets a message from Nya asking for reinforcements, and Lloyd finally goes on his first mission as the Green Ninja.
Meanwhile Kai and the others attempt to escape, but are quickly recaptured by Pythor who now has all four Fangblades.
The Serpentine want to celebrate with a Slither Pit tournament, which Pythor agrees to. Lloyd arrives but comically falls down right in front of Pythor. Just before he is captured, however, Garmadon arrives with the Skeleton Army. Lloyd frees the Ninja from their cage, and together they steal the four Fangblades and go back to Destiny's Bounty where Lord Garmadon leaves, making Lloyd upset.
The Ninja are having a party for Lloyd getting the Fangblades, but little do they know that Pythor is outside their very window, plotting revenge.
Unaware that Pythor has snuck aboard the Destiny's Bounty, the Ninja plan to throw the Fangblades into Torchfire Mountain. This fails when Pythor reveals his location to them, and steals the fangblades back, kncoking Master Wu off the deck and clinging to the side. Kai and the others just barely save him, and find that Pythor has escaped on a Rattlecopter with the Fangblades and takes control over a tour bus.
The Ninja intervene, and Kai fights off Serpentine on the top of the bus and is nearly knocked onto the road. Eventually Master Wu detaches the engine from the rest of the train and confronts Pythor, much to Kai's dismay.
The bus crashes into the Lost City of Ouroboros, halting the Ninjas' transportation. Fortunately, Lloyd arrives and takes them aboard the Destiny's Bounty. Just as Kai and the others attempt to save Master Wu, Pythor unleashes the Great Devourer. . .
After watching Wu and Pythor get eaten by the Devourer, Kai quickly leads the Ninja and the others back to the Destiny's Bounty. The Devourer chases them down, and the Ninja do all they can to ensure their escape. Unfortunately, the massive snake gets too fast, and they are forced to evacuate the Bounty.
The Ninja are forced to watch as the devourer, in one big bite, crushes the entire ship, and they run away.
As Jay begins to admit defeat, Kai inspires the team with some words of wisdom from Wu.
The team then heads to Ed and Edna's junkyard on their vehicles. It is there that Kai reveals the blueprints for the Ultra Sonic Raider. While there they discover that the Great Devourer has followed them, they use the Tornado of Creation to build the Raider out of all the scrap at the junkyard to defend themselves against it. In the battle, Kai discovers the Devourer has a weak spot on its forehead. The Ninja manage to drive it away from the area but Zane is injured during the conflict.
Realizing the serpent is heading to Ninjago City, Kai and the others follow it to its destination. While the creature begins destroying the city, the Ninja arrive and attack it. The fight is interrupted by the Ninja's Dragons returning as the Ultra Dragon.
Kai and the others cheer their respective Dragon on until the Devourer gains the upper hand and knocks it into a building. Lord Garmadon arrives and alerts the Ninja that the only way to truly destroy the Devourer is with the Golden Weapons, and he is the only one that is able to possess all four.
Kai is reluctant to hand him the weapons but eventually agrees. Kai and the others lead the snake around the city, eventually trapping it biting its own tail. The Ninja watch as Garmadon jumps from a building and strikes the creature's head with the weapons, causing it to explode into a mass of green goo.
Kai is annoyed when the Golden Weapons are nowhere to be seen, but rejoices when he discovers that Master Wu is alive. Victorious, the Ninja celebrate.